Central Station Air Handling Units are of sectionalized construction and each unit shall be complete with factory furnished components as shown on the plans. Casing panels are removable for access to the unit interior.

Major Unit Components

  • Supply Fan Section
  • Cooling Coil or Cooling/Heating Coil Section
  • Heating Coil Section
  • Filter Section
  • Mixing Box Section
  • Combination Angular Filter & Mixing Box Section
  • Sound Attenuator Section
  • Air Washer type Humidifier Section
  • Heat Recovery Section
  • Face & By-Pass Damper Section
  • Return Air Fan Section

The unit basic construction features a double skin casing with internal high density glass fiber or polyurethane insulation with total thickness of 25 mm. Structural members are made of extruded aluminum alloy with round edges.

The fan cabinet shall be an independent section joined to the companion sections. Fan section is designed for minimum noise level and efficient air movement without turbulence. Fan-motor assembly is truly isolated from the unit structure by means of anti-vibration mounts and canvas anti-vibration connections between fan and unit outlets. The section is equipped with:

  • Centrifugal double-width, double-inlet fan with galvanized steel scroll housing, with forwardly curved wheels for low and medium pressure applications, and with backward curved wheels for high pressure systems. Fan wheels are statically and dynamically balanced and keyed to rust protected solid steel shaft with permanently lubricated ball bearings. Maximum rated fan rpm is below the first critical speed.
  • Internally mounted TEFC IP54 fan motor suitable for ___ volt, __hertz, __ cycles electrical service installed on slide rails for belt tension adjustment on access panel side. Motor power shall be at least 20% higher than that required for fan operation at nominal air volume against total static pressure, which is the sum of the unit component static resistance and the specified external static pressure.
  • V-belt drive shall be designed for not less than 150% of motor nameplate horsepower. Motor sheave shall be easily removable and interchangeable. Motor sheave shall be adjustable allowing the fan speed to be regulated ± 10% of nominal fan speed.

Coils are constructed with round seamless ½" or 5/8" o.d. copper tubes and rippled corrugated aluminum fins spaced at 4,2 - 3,2 - 2,5 - 2,1 - 1,8 mm. The fins have full drawn collars to provide a continuous smooth secondary surface cover over the entire tube length. Tubes shall be arranged in a staggered pattern with respect to air flow and be expanded into the fin collar to insure continuous primary to secondary compression contact.
Coil casing shall be of continuous galvanized steel. Headers are of seamless copper tubing and water coils are circuited for counterflow heat transfer to provide the maximum mean effective temperature difference. Utilization of copper headers allows even thermal expansion and prevents any breaking risk, possible on steel headers. Testing pressure of water and evaporator coils set at 22 bar air pressure under warm water, suitable for operation at maximum 17 bar working pressure and 150 deg.C temperature.

  • CHILLED WATER COILS - Cooling Coils are designed for use with chilled water and are circuited completely drainable with a vent connection at the highest point and a drain connection at the lowest point.
  • DIRECT EXPANSION COILS - sweat type copper suction connections shall be located at the bottom of the suction headers for gravity oil drainage. Coils shall be circuited for (face control) (row control) capacity reduction. Pressure type liquid distributors shall be used.
  • WATER HEATING COILS - Heating coils will be constructed as above and will be at least two row in depth.
  • Drain pan is made of heavy duty galvanized steel, mastic coated.


  • Coating of the aluminum fins with epoxy phenolic resin can be offered for prevention of aluminum oxides appearing on the metal surface. This hydrophobic film has good anticorrosive properties and it is highly effective in minimizing salt corrosion.
  • Water spray humidifier
  • Water droplet eliminators, which become a standard item, if the coil face air velocity through the cooling coil exceeds 2,7 m/s.

Three different filter sections are available: flat, angular and bag-type filters. Each is compactly designed for maximum filter area, assuring a filter velocity for proper air cleaning regardless of filter media. Panel type filters in flat or angle arrangement are 50 mm thick, positioned in slide channels. Quick opening access panels on both ends simplify servicing. Filters in flat arrangement can be located in a common section with the coils and filters in angular arrangement in combination with the mixing box section. Panel type filters are EU-3 classification, as per EUROVENT 4/5 Standard( 80 to 85% WEIGHT ARRESTANCE as per ASHRAE STANDARD 52.76). Bag-type filters are class EU-5 classification ( 45 to 55 ATMOSPHERIC DUST SPOT EFFICIENCY as per ASHRAE STANDARD 52.76).


Mixing box consists of a plenum chamber provided with two air intakes, complete with control dampers. An additional section is available for air exhausting; in which case three control dampers are mounted. Damper assembly is of parallel-acting blades with interconnecting linkage and provided with motorized or manual control.

Splitter silencers suit any aspect ratio within the range and are in standard length of 900 mm, other lengths available according to attenuation requirements. Splitter frames are formed from pre-galvanised sheet steel. Absorbent material is resin bonded mineral fibre in slab form with erosion resistant facing. Splitters have a 200 mm standard splitter width and are mounted vertically. Inlet fairings fitted to the splitters reduce pressure losses. Airways between splitters are less than 100 mm width and the air velocity through airways for nominal unit fan volume flow does not exceed 10 m/s. Pressure drop at these conditions does not exceed 35 Pa. Low air velocities through airways avoid possible noise regeneration in the silencer even for 30 NC/NR level.
When the sound attenuator is located at the fan discharge, there is a 600 mm free distance between the fan discharge outlet and the splitters.